Recent electronic devices, typically mobile information terminals such as mobile phones, increasingly adopt light-emitting diodes or electroluminescent (EL) elements for lighting their control panels. This is to facilitate the identification and operation of buttons and display sheets, even in the dark. Movable contact units and switches that are easy to use and can be illuminated in diverse ways are also in demand in these devices.
A conventional movable contact unit and a switch are described next with reference to FIGS. 9 and 10. To facilitate understanding of the structure, dimensions are partially enlarged in these drawings. FIG. 9 is a sectional view and FIG. 10 is a plan view of the conventional switch. This switch includes movable contact unit 6, wiring board 67, light-emitting elements 69, and display sheet 70.
Movable contact unit 6 includes light-guide sheet 3, cover sheet 4, and movable contacts 65. Light-guide sheet 3 includes substrate 1 and luminescent portions 2. Film-shaped substrate 1 is light transmissive. Each of convex and concave luminescent portions 2 is provided in a predetermined area on the top face of substrate 1.
Cover sheet 4 is film-shaped, and each of movable contacts 65 is made of a dome-shaped thin metal sheet. Cover sheet 4 is attached to the bottom face of light-guide sheet 3 with adhesive (not illustrated) at predetermined portions of the outer periphery thereof. Each of movable contacts 65 is attached to the bottom face of cover sheet 4 under one of luminescent portions 2.
Wiring patterns (not illustrated) are formed on the top and bottom faces of wiring board 67. Fixed contacts 68 are provided on the top face of wiring board 67. Each of fixed contacts 68 includes substantially round central fixed contact 68A and substantially U-shaped or ring-shaped outer fixed contact 68B around central fixed contact 68A.
Movable contact unit 6 is attached to the top face of wiring board 67 such that the outer periphery of each movable contact 65 is placed on outer fixed contact 68B, and the center of the bottom face of movable contact 65 faces central fixed contact 68A with a predetermined distance in between.
Light-emitting element 69 is configured typically with a light-emitting diode. Light-emitting elements 69 are mounted on the top face of wiring board 67 at the side of light-guide sheet 3 so that a light-emitting face thereof is disposed facing the end face of substrate 1.
Film-shaped display sheet 70 is light transmissive. Light-shielding portion 70A and display portions 70B are formed on the bottom face of display sheet 70. Light-shielding portion 70A is formed typically by printing. Display portions 70B are formed by cutting out the shape of the characters, symbols, etc., on predetermined portions of light-shielding portion 70A. Each display portion 70B is disposed over luminescent portion 2.
The switch as configured above is placed on an operating face of the electronic device. Central fixed contacts 68A, outer fixed contacts 68B, and light-emitting elements 69 are connected to an electronic circuit (not illustrated) of the electronic device via wiring patterns or the like.
When a user presses display sheet 70 at a position corresponding to one of display portions 70B, light-guide sheet 3 and cover sheet 4 dent, and a dome-like center of movable contact 65 is pressed. When a predetermined pressing force is applied to this center, movable contact 55 resiliently inverts downward with a click feeling, bringing the center of the bottom face of movable contact 65 down into contact with central fixed contact 68A. This contact electrically connects central fixed contact 68A and outer fixed contact 68B via movable contact 65.
When the user releases the pressing force on display sheet 70, movable contact 65 resiliently reverts upward due to its resilient recovery force. As a result, the center of the bottom face of movable contact 65 separates from central fixed contact 68A, and central fixed contact 68A and outer fixed contact 68B are electrically disconnected. The device is switched to each function by electrical connection and disconnection of fixed contact 68.
When power is supplied to light-emitting element 69 from the electronic circuit of the device, light-emitting element 69 emits light. This light enters light-guide sheet 3 from its end face, and propagates inward through light-guide sheet 13, causing a reflection in substrate 1. This light is further diffused and reflected in luminescent portion 2, and illuminates display portion 70B from beneath. The user can thus identify the indications on display portions 70B, such as characters or symbols, even if the surrounding area is dark. Accordingly, the user can operate the device with ease. This type of movable contact unit is disclosed, for example, in Japanese Patent Unexamined Publication No. 2007-87749.
In above conventional movable contact unit 6 and switch, the light of light-emitting elements 69 enters substrate 1 from the end face, and luminescent portions 2 emit light at once so as to illuminate each display portion 70B. Accordingly, display portions 70B are illuminated at once in only one luminescent color.